The purpose of this project is twofold: (1) improvement of the understanding of physiological changes that occur during and after endotracheal aspiration; and (2) generation of a set of procedural guidelines which determine an optimal method of endotracheal aspiration. Anesthetized male dogs, weighing between 18 and 30 kg will be utilized in order to determine respiratory and cardiovascular responses to various levels of suction, hyperinflation, and hyperoxygenation. Variables measured before, during, and/or after suction will include: arterial and mixed venous oxygen tension, carbon dioxide tension, and pH: alveolar-to-arterial oxygen tension difference; arterial-to-venous oxygen tension difference, shunt fraction; physiologic dead space; carbon dioxide production, lung-thorax compliance, right and left atrial pressures, pulmonary arterial pressure, aortic pressure; and electrocardiogram. Results of this study will contribute not only to the improvement of clinical procedures currently in use but also to the generation of new information regarding the effects of suction, hyperinflation, and hyperoxygenation on the cardiovascular system.